Injury Severity Score (ISS) Calculator
Calculate ISS for trauma severity using AIS scores across six body regions. Free online medical calculator with breakdown and charts for healthcare professionals.
About This Calculator
The Injury Severity Score (ISS) is an internationally recognized anatomical scoring system that assesses trauma severity in patients with multiple injuries. Developed by Baker et al. in 1974, the ISS correlates with mortality, morbidity, and hospitalization time after trauma, making it an essential tool in emergency medicine, trauma surgery, and intensive care.
The ISS divides the body into six regions: Head/Neck including cervical spine, Face including the facial skeleton, Chest including thoracic spine and diaphragm, Abdomen and pelvic contents including abdominal organs and lumbar spine, Extremities and pelvic girdle, and External/skin. For each region, an Abbreviated Injury Scale (AIS) score of 0 (no injury) to 6 (maximal/unsurvivable) is assigned based on the most severe injury in that region. The ISS is calculated by squaring the three highest AIS scores from three different body regions and summing these squares. If any single AIS score is 6, the ISS is automatically set to 75. The final score ranges from 0 to 75, with higher scores indicating greater injury severity.
The ISS is used worldwide in emergency departments, trauma centers, and by emergency medical services (EMS) for patient triage, prognosis prediction, outcome research, and quality improvement in trauma care. An ISS greater than 15 defines major trauma (polytrauma), which typically warrants treatment at a dedicated trauma center. The ISS also serves as a key inclusion criterion in trauma research studies and is used for benchmarking trauma center performance across institutions and countries.
Regional Notes
India: ISS is used across major trauma centers and AIIMS-level hospitals for trauma triage and research. The National Programme for Trauma Care (NPTC) supports standardized trauma scoring. India faces a high burden of road traffic accidents — a leading cause of major trauma — making ISS assessment critical for emergency preparedness.
United States: The ISS is integral to the American College of Surgeons (ACS) Trauma Quality Improvement Program (TQIP). It is used in all Level I and Level II trauma centers for benchmarking and outcomes research. The National Trauma Data Bank (NTDB) uses ISS for risk-adjusted mortality analysis.
United Kingdom: The Trauma Audit and Research Network (TARN) collects ISS data from all major trauma centers in England and Wales for performance monitoring and research. The National Institute for Health and Care Excellence (NICE) recognizes ISS in major trauma management guidelines.
Frequently Asked Questions
What is the Injury Severity Score (ISS)?
The Injury Severity Score (ISS) is an anatomically-based scoring system that assesses trauma severity by dividing the body into six regions — Head/Neck, Face, Chest, Abdomen/Pelvic Contents, Extremities/Pelvic Girdle, and External. Each region receives an Abbreviated Injury Scale (AIS) score from 0 (no injury) to 6 (maximal/unsurvivable). The ISS is calculated by squaring the three highest AIS scores from three different body regions and summing them, with scores ranging from 0 to 75. An ISS greater than 15 is classified as major trauma.
How is the ISS score calculated?
To calculate the ISS, assign an AIS score from 0 to 6 for each of the six body regions. Take the three highest AIS scores from three different body regions, square each score, and sum the squares (ISS = A² + B² + C²). If any single AIS score is 6 (maximal/unsurvivable), the ISS is automatically set to 75. For example, if the three highest AIS scores are 4 (severe), 3 (serious), and 2 (moderate), the ISS would be 16 + 9 + 4 = 29.
What does an ISS score of 15 mean?
An ISS score of 15 is the threshold for defining major trauma (polytrauma). Scores of 15 or below are classified as mild to moderate trauma, while scores above 15 indicate severe to very severe injury. An ISS of 16 to 24 is classified as severe, and 25 to 75 as very severe or critical. The ISS correlates with mortality risk, morbidity, and hospitalization time after trauma.
What is the Abbreviated Injury Scale (AIS)?
The Abbreviated Injury Scale (AIS) is an anatomically-based consensus-derived global severity scoring system developed by the Association for the Advancement of Automotive Medicine (AAAM). It classifies each injury on a six-point ordinal scale: 1 (Minor), 2 (Moderate), 3 (Serious), 4 (Severe), 5 (Critical), and 6 (Maximal/Unsurvivable). The AIS covers nine body regions including Head, Face, Neck, Thorax, Abdomen, Spine, Upper Extremity, Lower Extremity, and External.
Can this calculator be used for clinical decision-making?
This calculator is intended for educational and reference purposes only. It should not replace professional medical judgment or clinical decision-making. The ISS is a validated scoring system used worldwide in trauma centers, emergency departments, and by emergency medical services (EMS) to assess injury severity, triage patients, and predict outcomes. Always consult a qualified healthcare professional for medical advice and treatment decisions.
What is the difference between ISS and New Injury Severity Score (NISS)?
The New Injury Severity Score (NISS) is a modification of the ISS that takes the three highest AIS scores regardless of which body region they come from, while the ISS requires the three highest scores to come from three different body regions. The NISS was developed because patients can have multiple severe injuries within the same body region (e.g., two AIS 5 injuries to the chest), and the ISS would only count one of them. Research suggests NISS may better predict mortality in some patient populations.
What are the limitations of the ISS?
The ISS has several limitations. It does not account for multiple injuries within the same body region (addressed by the NISS), does not consider physiological parameters like blood pressure or GCS, does not include age or comorbid conditions, and cannot differentiate between injury patterns across different mechanisms. The ISS also assigns equal weight to all body regions, which may not reflect the true impact of injuries to different anatomical areas. For comprehensive trauma assessment, the ISS should be used alongside other scoring systems like the Revised Trauma Score (RTS) and TRISS methodology.